Newly built PC no signal to monitor keyboard or mouse

Hello, so I've come to this unexpected problem: just built my new pc, everything done by the tutorial, everything seemed to be fine. But when I started the pc I only got the fans spinning and nothing else. Monitor is not showing anything, mouse and keyboard as well. I almost checked everything: checking rams, trying with only 1 ram, checking all the cables, taking out the cmos battery, plugging in the speaker to hopefully get any sound but with no success. I honestly don't know what to check anymore. Hopefully someone can help me with this stupid problem. My PC specs: MOBO: GIGABYTE B450M DS3H V2
CPU: AMD Ryzen 5 5600G
RAM: Patriot Viper 4 DDR4 16GB kit
Also, if it has anything to do with this problem, my case came in with a torn power led - cable, but I dont think it is the problem. Also I didnt mention my GPU, cuz I plugged gpu from my older computer. Just in case the gpu is AMD Radeon R7 370 2GB or whatever. Just to give more information, when I started the pc all fans were spinning, except the gpu fan. I know gpu fans are not supposed to spin all the time, but when I started my older pc with this gpu the fans were spinning when pc is started and then stopped. When GPU is inserted to this new build it seems like gpu is not working or basically the fans of the gpu are not spinning for some reason. Hope someone can help me with this problem. Sorry for my bad english.